The present invention generally relates to material handling systems and more specifically, but not exclusively, concerns a three-dimensional material handling system as well as techniques for utilizing the system.
Picking products in distribution centers for order fulfillment has historically been one of the most labor intensive processes. The picking activities are monotonous for human operators. This leads to quality issues (like mis-picks), high employee turnover, and inconsistent productivity. Moreover, some environments can be unpleasant or even hazardous to human operators, such as commercial freezers that are used to store food. Turnaround time for both warehousing and removal is still yet another concern. The quicker that goods can be processed and loaded onto trucks, trains, or other transports, the larger geographical area a distribution center can service. For example, the quicker a truck can be loaded and unloaded, the larger a service territory the distribution center is able to service because the truck can cover a greater distance in the same amount of time. Another ongoing issue for product distribution systems is product warehouse space. As the cost of real estate continues to increase, minimizing the footprint of the warehouse becomes an even greater concern.
Most warehouses only utilize a fraction of their available vertical space due to many factors, including the limited range to access items stored at higher levels. Three dimensional rack systems in the form of Automated Storage and Retrieval Systems (often referred to as ASRS or AS/RS) have been proposed that store items on vertical storage racks. However, these vertical systems have several significant commercial drawbacks. As one example, throughput is always a concern for these vertical systems because moving the additional vertical dimension can increase retrieval times. In other words, retrieving items from the racks in a quick and efficient manner has been a constraint in most proposed systems. Moving items in the racks to a position where they can be retrieved has also been a concern. To address this issue, the racks are typically very narrow and usually are designed to store one or two pallets or cartons at most. Thus, the capacity for a given rack is significantly reduced, which in turn reduces the storage space utilization or efficiency. In addition, the technological complexity of these systems tends to cause significant downtime as well as increased maintenance expenses. Due to the complex and automated nature of typical ASRS implementations, these systems tended to be rigid as to how the items are handled and the types that can utilize the systems. Such systems typically are only able to handle pallets or cases with fixed dimensions, which in turn limits their flexibility.
Generally speaking, items from the racks can be fed either using a gravity feed or powered system. An example of a gravity feed system is what is termed an “A-frame” type storage rack. Typically, A-frame racks store items that are light and not easily crushed like pharmaceutical products. While useful in limited situations, A-frames cannot be used with larger items and/or fragile items, such as electronics, food, etc. On the other hand, powered systems can store larger items on generally flat conveyor belts. Given that the conveyors are generally flat, the items can be spaced apart so as to avoid damage caused by items knocking into one another. However, powered rack systems are not economically practical because of the large number of motors required for each conveyor in the stack. Conveyor motors are expensive, and each level in a vertical stack can include multiple separate conveyors that are individually operated by the conveyor motor. As should be recognized, the costs associated with the conveyor motors multiplies as the number of stack levels increases. Moreover, with the large number of motors involved, the risk of at least one of the motors failing increases. In addition, ancillary expenses, like performing routine preventive maintenance on the motors, can make such systems cost prohibitive.
Thus, there is a need for improvement in this field.